"THAT is sick. You are so sad,” said 12-year-old Roscoe. Our guilty secret was out. We, a pair of middle-aged crusty old parents, were going to see the new Inbetweeners film, about a group of four, hapless, sex-obsessed teenage boys going off on a lads’ holiday abroad.

Our 19-year-old, who was heading off on a lads’ holiday abroad, didn’t want us to see it either: “Whatever you do, don’t watch that film until I get back from Bulgaria,” he warned us. “You’ll only worry.”

We got hooked on the shockingly crude Channel 4 programme that the film is based on about a year ago.

Once you get past the foul language, vulgar sexual references and the toecurling, eye gouging embarrassment of the boys’ puerile antics, it is also incredibly funny and heartwarming.

And as parents of teenage boys, despite the fact that much of it makes us shudder with anxiety, it is also worth watching because it provides such a brilliant, piercing insight into their lives and minds. Trapped between childhood and manhood, they are trying to find their way in a world that is exciting and terrifying at the same time.

We can all remember being that age, desperately trying to act like we knew what we were doing when we were actually pretty clueless. The storylines are littered with drunken disasters, woeful chat-up lines, awkwardness around the opposite sex and clumsy sexual activity. The boys are always saying the wrong things, wearing the wrong clothes, getting off with the wrong girl.

And we recognise so many of the characters – from the loudmouth fantastist Jay, whose preposterous boasts about everything from girlfriends to how far he can swim fool no-one, to hopeless Romantic Simon, who wears too much hair gel. Then there’s square but painfully earnest Will, who wears the wrong trousers and carries a briefcase to school, and dim Neil who, despite his intellectual failings, manages, inexplicably, to pull all the girls.

The cringeworthy parents are painfully recognisable too, from the dad who embarrasses his son by insisting on being “one of the lads”, talking at length about the sexual conquests of his youth in front of his friends, to the yummy mummy divorcee whose boyfriend drives a sports car.

Unlike the arty and pretentious TV teen series, Skins, where the teenagers are scarily cool and unrealistic, the Inbetweeners, set in the fictional Rudge Park Comprehensive, has the uncomfortable, acneridden ring of truth about it.

It might be much more near the knuckle, but it takes me back to Bill Forsyth’s classic schooldays film, Gregory’s Girl, with its charming evocation of how it really feels to be a teenage boy and all the anguish, heartache and humiliation, as well as moments of sheer joy, that that entails.

Probably because it is so realistic, our boys won’t let us watch it in the same room as them at home. It’s much too painfully embarrassing for them and, if I’m honest, for us.

That is why we left it a few weeks before going to see the film, imagining that most teenagers, like our older boys, would all have been to see it by then.

Unfortunately, the place was full of would-be Jays, Wills, Neils and Simons.

But there were also quite a few sheepish looking middle-aged parents like ourselves, eyeing each other up self-consciously.

The film wasn’t quite as good as the series. The script was too obvious, the female characters too one-dimensional, and it probably went on too long. But still, we howled with laughter and cringed with embarrassment at the same time.

My husband felt sorry for the youngsters sitting next to us: “I don’t think they really want to listen to you sitting next to them, tutting and sighing through all the rude bits,” he barked at me. I didn’t even realise I was doing it. That’s middle age for you.

Amazingly, some parents had come along with their teenage children.

I wouldn’t advise this.

And neither would I advise you to watch it if your children have not yet reached their teenage years. You still have all of this to come. It will only terrify you.

LIKE a scene straight from the Inbetweeners, our 19-yearold was boasting, when he returned from his lads’ holiday in Bulgaria, that he and his friends’ escapades had been much wilder than anything that happened in the film. His brothers laughed at him. “No really, really,” he said, sounding like the hopeless braggart Jay. “Two of the boys were nearly arrested and one of us was hospitalised. You don’t get much wilder than that.” His girlfriend, who had been listening, gave him a withering look: “Being nearly arrested for weeing in the street is hardly wild. And going to hospital with conjunctivitis is just sad,” she said, shaking her head.